Titanium base alloy



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' nGmq TIME HOUI' S AGIN TEMPERATURE-Q00 F QINVENTOR WARREN M. Pan-ems .Y l/gulbafirghfimnmon, M,M+JW

United States Patent No. 346,142, 3, 1966, Ser.

ABSTRACT OF THE DISCLOSURE An age hardenable, metastable beta titanium base alloy containing 9-ll% vanadium, 7-8.5% chromium, 2.4- 32% aluminum, up to 0.2% in total amount of carbon, oxygen and nitrogen, balance titanium with incidental impurities.

This application is a continuation-in-part of my copending application Ser. No. 346,142, filed Feb. 20, 1964, now abandoned.

This invention pertains to metastable beta titanium-base alloys which as solution treated and quenched from above the beta transus have a substantially all-beta structure, but upon reheating to some temperature below the beta transus are age hardenable by precipitation of alpha nuclei in thQ'bCtfi matrix.

Although such age hardenable, beta type alloys in general'possess unique and useful properties, particularly good cold formability, ability to be aged to high strength levels and deep hardening in heavy sections, the previously known types, such as the commercial grade Ti-13V-1lCr- 3A1, possess some serious disadvantages. One of them is that they require relatively long aging times to reach full aged strength. Another is that owing to their high alloy content, heating to relatively high temperature is required during fabrication into mill products. High processing temperatures in the mill are disadvantageous by reason of increased wear and tear on equipment, and increased surface oxidation, productive of surface imperfections which are difiicult to remove.

The present invention provides an age hardenable, beta type titanium alloy of substantially lower alloy content than previously known grades, and one which reaches its full aged strength in a much shorter time, especially from a fully annealed initial state. In addition the alloy of the invention may by reason of its relatively low alloy content be fabricated into mill products at lower temperatures and pressures than heretofore required for processing known types of beta alloys.

The age hardenable, beta type titanium base alloy of this invention consists essentially of from 9% to 11% vanadium, from 7% to 8.5% chromium, 2.4% to 3.2% aluminum, and the balance titanium with incidental impurities. A preferred alloy according to this invention consists essentially of about vanadium, about 8% chromium, about 2.8% aluminum, and the balance commercial titanium sponge.

The single figure of the accompanying drawing compares the aging response of the alloy of this invention with that of the commercial Ti-l3V-11Cr-3Al grade from an initially fully annealed condition of each.

The amounts of the various alloying elements in the beta type titanium base alloy of this invention are critical. The total amount of beta stabilizers, that is the vanadium and chromium, is important. Too low an amount of these elements in the aggregate will not provide enough total beta stabilizer so that a beta type titanium base alloy is produced. Too low a beta stabilizer content will cause the alloy to lose its depth of hardening capability. On the 3,409,428 Patented Nov. 5, 1968 other hand, too great a total amount of beta stabilizer, i.e., wherein the sum of vanadium and chromium is more than 20%, will slow down the strengthening and hardening elfects of aging and make hot and cold working difiicult. A stable all-beta titanium alloy composition does not possess appreciable hwt treatability. Actually, the beta type alloys as employed commercially are of metastable composition such that they can precipitate out some alpha phase titanium on aging, but the amount and dispersion of alpha phase must be small and carefully controlled so that the characteristics of the beta type alloy are preserved to the fullest extent. Therefore, to accomplish the purposes of the alloy of this invention, the sum of the vanadium and chromium should lie between a minimum of 16% and a maximum of 20% with the ranges of vanadium and chromium individually as hereinbefore defined.

The relative amounts of vanadium and chromium in the alloy of this invention are important to provide a V to Cr ratio having a beta transus at a desirable temperature for imparting to the alloy capability for most eflicient mill processing, at the same time providing excellent mechanical properties.

The aluminum content of the alloy of this invention is also critical and should range as described above, between 2.4 and 3.2%, and preferably should be about 2.8%. This amount of aluminum is important to suppress omega embrittlement, but at the same time provides sufficient amount of an alpha stabilizing element so that there will be some precipitation of the alpha phase during aging. The effective range of the aluminum content is narrower than the ranges for vanadium and chromium because the effect on phase stability of aluminum and alpha stabilizer is very much greater than the effect of vanadium or chromium on the beta phase. The aluminum content of the alloy of this invention should be at least 2.4%. Less than this amount will not provide suflicient alpha phase to provide the advantages of heat treatment and ability to be aged to high strength in a reasonable time. More than 3.2%} aluminum will provide an excess of alpha stabilizer and the alloy will lose much of the advantages of the allbeta alloy composition.

Incidental impurities may be present in the alloy of this invention in amounts below the level which will affect the nature and properties of the alloy, and should in general not exceed in the aggregate about 0.4%. This will include the interstitials, oxygen, nitrogen and carbon which as a separate group should not exceed about 0.2%, and of these the oxygen content appears to be the most critical and determined on the alloy in ingot form should not individually exceed 0.16%. Such impurities may be introduced as impurities in the titanium and alloying metals used and may also be picked up during melting and processing.

An important characteristic of the alloy of this invention is its ability to reach maximum aged strength from the full annealed condition on aging for a period of 8 hours at 900 F. This effect will be readily seen from the drawing which, as above stated, compares the aging response of the preferred Ti-10V-8Cr-3Al alloy of this invention to that of the commercially produced beta alloy, namely, one comprising 13% vanadium, 11% chromium, 3% aluminum and balance titanium. As will be seen from the drawing, the yield strength (0.2% offset) of the Ti-l0V-8Cr-3Al alloy of this invention plotted as curve 1 increases rapidly with aging time reaching a maximum after about 10 hours at 900 F. Curve 2, which shows results obtained in similar fashion for the Ti-13V-l1Cr-3Al alloy, does not rise as steeply and at the end of 32 hours has reached a strength level of only 180,000 p.s.i. and would require aging for perhaps 48 to 60 hours to reach 200,000 p.s.i. In addition, it will be seen from the drawing that after 10 hours the aging response curve for the Ti-10V-8Cr-3Al alloy is essentially fiat or level while that for the heretofore produced Ti-l3V-1lCr-3Al alloy continues to rise at least to some Results of tensileand notch bend properties are shown in Table 3 below.

TABLE 3.-TENSILE AND NOTOH BEND PROPERTIES OF degree over a test period of many hours. For this reason, 5 0050110011 GAGE 001.1) ROLLED snnis 'r FROM HEAT the aged strength of the alloy of this invention may be xfiig 'gi gjg ggffl AT 1,590 MIN) closely controlled and accurately predicted whereas final aged strength in all beta alloys formerly used was much Nominal Compositiom THOWBOHAI; Heat ow- 507- more dependent on heat treating time which had to be A i Tim T t U 0 7 8 E N t h 2 gng e es o c carefully controlled to capture desired properties. 10 Hours Din m, I 12.5.1. Peree'nt Bend R/t.

Attainment of full aged strength in the alloy of this invention after less than 10 hours at aging temperature 0 L provides a significant processing saving over the cost of aging alloys requiring an aging time of the order of two '1 or three times as long. 2 g The following example illustrates the production of '1 the alloy of this invention and processing and test proce- 4 E dures to determine its mechanical properties. '1 EXAMPLE 5 L L Sufficient virgin titanium sponge of oxygen content less than 0.08% was admixed with pure subdivided chromium 8 I: and aluminum and 85% V-lSAl master alloy to produce T an alloy comprising 10% V, 8% Cr and 3% Al balance 16 E titanium. The mixture was pressed into compacts which L were melted in a consumable electrode arc melting '1 '1 furnace under vacuum to produce a 20 lb. ingot of alloy. 24 0 L Analysis of the ingot showed the following. TABLE 1.-INGO'1 v-2507 V or, A1 or i To produce 100% recrystallization. Percent Percent Per'cent Percent iglg ggg fi fig ggg fgg 9 94 05 3. 20 4 Smallest radius die available: 9. 94 7.64 3.20 (4 samples). 10.02 7.01 a. 12 5 o Another important characteristic of the alloy of this in- .Average 10.03 7.87 3.15 0.124.

vention is its improved hot rollability. This was determined by rolling sheet from alloy bars of the alloy of this invene After conditioning the mgot was forged to 3 Inch Squ'flr tion and also a commercial all-beta titanium alloy combar and sections of the bar were rolled to sheet according to the Schedule in Table 2 40 prising 13% vanadium, 11% chromium and 3% aluminum. The deflections of the rolls was carefully measured TABLE 1411M? V4507 1N GOT during rolling of sheets varying from 0.10 inch to 0.45 Fo e .0 11w?! Squaw] inch in thickness. Rolling the alloy of this invention re- Cut 1"Th1ilck Transveris e slices. gig 'rr i i i l a isve r s sulted in an average of 0.005 inch less roll deflection than U set R0 at 1,750 o 0.230 0 0 a .w @hick and Anneal 1,750. K (10 opsming 1 Measum was determined during rolling of the 13y 1101' 5A1 alloy min.) AC. I, Thickness. This demonstrates that the alloy of this invention is apam? and Pmkm Ofi preciably easier to roll. Of possibly more significant interg R011 0 g-gj%- i6 i fif g agi g fi ggg est is that easier to roll characteristics would permit 0 Zi c. Mum 0 130 tisoa cieo, and 0. 075" equivalent rolling efficiency at lower temperature and this 11655 easuremen S. Sandblast and Pickle .010" Ofl Determine Relative Hot Rollecou1 d liesult m slglzlficantly less surface contammatl9n Gage. bih y (fi 1 (oxidation) which is a normally and well known disgtgl iigl P1350553 e or advantageous feature of an all-beta type titanium alloy. X' aw g E ai Mill roll deflection data for Heat V-2507 is shown in 6 S 123%.? Tesi, Te sile, Notch Table 4 below compared with an alloy containing 13% Ben v, 11% Cr and 3% A1.

TABLE 4 Mill Actual Difier- Sheet Nominal Opening, Sheet ence, Width, Composition Inches Gage, Inches Inches clies N i-2507 Ti-10 v-s (Jr-3 Al-.... 0.650 0.673 0.023 3.187

0. 450 0. 479 0. 029 0.300 0.331 0. 031 0.150 0.185 0.035 0.075 0.112 0.037 7-2451 Ti-13 V-11 Cr-3 AL-.- 0 660 0.077 0.027 3.125

The alloy of this invention may be produced by any convenient method in which the titanium and alloying elements are melted together to form a substantially homogeneous composition. Preferably, titaniumsponge of required purity, and particularly with respect to its oxygen content, is admixed with subdivided chromium, vanadium-aluminum alloy and aluminum of the required purity, in proper amounts and the mixture is then compressed into compacts. These compacts are welded together to form an electrode which is melted in a consumable electrode arc melting furnace to produce an ingot of alloy. The so produced alloy ingot may itself be employed as an electrode in a subsequent remelting step to provide improved homogeneity in the final alloyed ingot.

The alloy of this invention is useful for producing aircraft and missile parts where light weight and strength are desirable characteristics. It is particularly useful when produced as a mill product such as bar, sheet, strip, etc. and which is further fabricated by a forming operation. The alloy of this invention will be found to be light, strong and readily formed as well as possessing the unique aging and rollability properties hereinbefore discussed.

The alloy of the invention is particularly valuable as a sheet or strip alloy of superior producibility to that of the commercial Ti-13V-1lCr-3Al grade. As such, one of its important advantages is that of its fast aging response in the fully annealed condition. It is well known in the art that the aging kinetics of any metastable beta alloy are accelerated by any residual cold work in the material when it is aged. In other words, any cold worked or only partially annealed sheet material of such an alloy will age harden at a faster rate than a fully annealed one. In this condition, however, one of the major desirable properties of a beta alloy sheet, namely its excellent formability, is compromised. Also, such sheet material in the partially annealed condition is more difficult to produce because it requires very close control of rolling and annealing schedules to produce the best compromise between a reasonable aging rate and an acceptable formability.

The commercial grade, Ti-13V-11Cr-3Al, in sheet form is generally produced in a partially annealed condition because of its slow aging response after full annealing. In the accompanying drawing, the graph shown for the Ti- 13V-11Cr-3Al commercial grade, is typical of fully annealed sheet material of this composition. Likewise, the graph shown for the Ti-1OV-8Cr-3Al alloy of the present invention, also typifies fully annealed sheet material thereof, which as seen from the foregoing, is more readily producible and is in the condition giving maximum formability. The aging response for the commercial Ti-13V- 11Cr-3Al grade, may be increased by subjecting the material to heavy cold reduction prior to aging. But in this condition, such sheet material will have little or no formability, and is thus objectionable in this regard.

I claim:

1. An age hardenable, titanium base alloy consisting essentially of about: 9 to 11% vanadium, 7 to 8.5% chromium, 2.4 to 3.2% aluminum, up to about 0.2% in total amount of carbon, oxygen and nitrogen, balance titanium with incidental impurities, characterized as fully annealed in its ability to attain substantally its maximum aged 0.2% olfset yield strength of about 190,000 p.s.i. on aging for about 10 hours at 900 F.

2. A titanium base alloy according to claim 1 consisting substantially of about: 10% vanadium, 8% chromium, 3% aluminum, up to 2.0% in total amount of carbon, oxygen and nitrogen, and the balance titanium with incidental impurities.

References Cited UNITED STATES PATENTS 2,892,706 6/1959 Jaffee -1755 9/1964 Vordahl 75--175.5 

